Outdoor Circuit-Rcd Protection

Discussion in 'Electricians' Talk' started by iain.p, Jun 12, 2019.

  1. iain.p

    iain.p New Member

    I am planning to install an outdoor circuit for lighting and a water butt pump, Total load under 13amps, I am not an electrician but I have reasonable knowledge.

    I will be using 1.5mm Swa cable 3 core approx. 40 metres long (so I can take it under ground or above if needed) adding in 3/4 Ip66 outdoor sockets along the way, as I mentioned above I am not an electrician so I will power the circuit from the garage by using a 13amp plug directly into the ring main which is protected by an Rcd on the downstairs ring main (80A 30mA)in the house Cu, this way I will not cause any problems in the future as it can be unplugged when not required.

    My main problem/question is should the Rcd (in the Cu) trip out. this will knock out the fridges/freezers etc on the same circuit-so should I add a separate Rcd adaptor/plug.

    Normal surface mounted 2 gang socket in garage ---- Rcd adaptor? ----13amp plug ----40 metre Swa cable with weather proof sockets

    The adaptor will have the same trip current of 30mA as the Rcd on the Cu.so will they both trip out or is there another way of doing this.

    Any help suggestions, advice welcome.

    Thank you Cu 2019.jpg2.jpg Cu 2019.jpg2.jpg Cu 2019.jpg2.jpg
  2. Coloumb

    Coloumb Screwfix Select

    From what your saying you plan to run an extension lead from a socket that the fridges/freezers share a 30ma RCD on. If this is the case then yes if the extension lead causes the RCD to trip then it will also disconnect the fridges/freezers. You can't fit an additional 30ma RCD to just the extension lead, this won't stop the upstream RCD from tripping You would have to redesign your setup using RCBO's. Time delayed RCD's might be an option but would be very complicated to setup and still be within 7671.

    I would suggest getting a spark in, he will be over the moon if you do the trenching for him.
  3. Peterdevon

    Peterdevon Active Member

    Need to look at at PV on the same RCD as the sockets because of it's shut down time being greater than the 40 mS
  4. dobbie

    dobbie Screwfix Select

    Get an Electrician in to do the job properly.
    As a side note,you cannot terminate an swa cable into a 13a plug top as you intended.
  5. iain.p

    iain.p New Member


    Thank you for your quick reply's.

    I think that i will call in the Pro's to take a look at the Pv and outdoor circuit addition, as i want it safe and to code,

    instested to know why i cannot terminate swa at a 13a socket,if its inside an internal garage, your thoughts? (always keen to learn from the Pro's)

    Thanks again
  6. Coloumb

    Coloumb Screwfix Select

    The steel on the SWA needs to correctly earthed which requires the use of a gland. Ergo, it is technically not possible to terminate SWA into a 13a plug, although I've seen some lash-ups using an earthing clamp.
  7. iain.p

    iain.p New Member

    i see, makes sense, digging and garden come to mind.
  8. Pollowick

    Pollowick Screwfix Select

    Get a local pro in to do it.

    Agree with him what needs doing, he supplies the cable, you dig the trench, lay the cable (and backfill when all complete), clip the cable, put loops where the sockets wil go, and the other donekey work. He adds to CU, fits sockets, terminates SWA &c.
  9. Bazza

    Bazza Screwfix Select

    [pedant]You can’t terminate it into the bottom of the plug either![/pedant]
  10. Hans_25

    Hans_25 Screwfix Select

    1.5mm SWA looks a bit small to me, for 40m. Spark will do the calcs and advise.
  11. Bazza-spark

    Bazza-spark Screwfix Select

    You can't terminate SWA into a plug, but you can into a socket or an adaptable box. You need to ensure that you fit the banjo and connect the armour to earth via that, or use an earthing nut.

    As for the circuit, you could protect it with a 10mA RCD which should trip before the main 30mA one.

    Kind regards
  12. Bazza

    Bazza Screwfix Select

    It probably won’t. Given a fault of >30mA (most are) they’ll probably both trip. You can only reliably discriminate RCDs on the basis of time, not current.
  13. W. Axl Rose

    W. Axl Rose Member

    Completely incorrect.
    Póg mo thóin likes this.
  14. unphased

    unphased Screwfix Select

    Yes you are right, unusually. A 10mA RCD would not discriminate with a 30mA RCD and it is pointless using it. Clearly.
  15. W. Axl Rose

    W. Axl Rose Member

    Nothing unusual about it.
    Póg mo thóin likes this.

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